LC sensors are well known in the art. For example, LC sensors may be used as electronic proximity sensors which are able to detect the presence of a conductive target. Some common applications of inductive sensors include, e.g., metal detectors and derived applications, such as rotation sensors.
FIG. 1 shows a typical LC sensor 10. Specifically, in FIG. 1, the LC sensor 10 comprises an inductor L and a capacitor C, which form a resonant circuit also called a tank circuit. The arrangement comprises a power supply 102, such as a voltage source, and a switch 104.
When the switch 104 is in a first position as shown in FIG. 1, the capacitor C is charged up to the supply voltage. When the capacitor C is fully charged, the switch 104 changes position and places the capacitor C in parallel with the inductor L and starts to discharge through the inductor L and initiates an oscillation between the LC resonant circuit 10.
From a practical point of view, the LC sensor 10 also comprises resistive components R, which will dissipate energy over time. Accordingly, losses occur which will decay the oscillations, i.e. the oscillation is damped.
Basically, such LC sensors 10 may be used, e.g., to detect metallic objects, because the oscillation may be damped quicker in the presence of a metallic object (see e.g., FIG. 2b) compared to an oscillation without a metallic object (see e.g., FIG. 2a).
Generally, the sensing component of an LC sensor 10 may be the inductor L, the capacitor C and/or the resistor R. For example, the resistance R influences primarily the damping factor, while the L and C components influence primarily the oscillation frequency.
Moreover, an LC sensor 10 may also be created by coupling a capacitor C to an inductive sensor L or an inductor L to a capacitive sensor C. However, usually the inductor L (with its dissipative losses) constitutes the sensing element.
FIG. 3a shows a possible example for performing the LC sensing of the sensor 10 with a control unit 20a, such as a microcontroller described in the documents Application Note AN0029, “Low Energy Sensor Interface—Inductive Sensing”, Rev. 1.05, 2013 May 9, Energy micro, or Application Report SLAA222A, “Rotation Detection with the MSP430 Scan Interface”, April 2011, Texas Instruments.
In the example considered, the control unit 20 comprises two pins or pads 202a and 204a, and the LC sensor 10 is coupled between these pins 202a and 204a. 
Substantially, the control unit 20a comprises a controllable voltage source 206a coupled to the pin 202a in order to impose a fixed voltage VMID at this pin 202a. For example, usually a digital-to-analog converter (DAC) or a dedicated voltage source is used for this purpose.
During a charge phase, the pin 204a is coupled to ground GND. Accordingly, during this phase, the sensor 10 is coupled between the voltage VMID and ground GND and the capacitor C of the sensor 10 is charged to the voltage VMID.
Next, the control unit 20a opens the second pin 204a, i.e. the pin 204a is floating. Accordingly, due to the fact that the capacitor C of the sensor 10 has been charged during the previous phase, the LC resonant circuit 10 starts to oscillate as previously described.
Thus, by analyzing the voltage, e.g. voltage V204 at pin 204a, the oscillation may be characterized. In particular, as shown in FIG. 3b, the voltage at the pin 204a corresponds to a damped oscillation having a DC offset corresponding to the voltage VMID, imposed by the voltage source 206a, i.e. the voltage VMID constitutes the middle point of the oscillation.
Accordingly, the voltage VMID is usually set to half of the supply voltage of the control unit 20a, e.g. VDD/2, in order to have the maximum range.
Often, the circuit also comprises an additional capacitor C1 coupled between the pin 202a and ground GND in order to stabilize the voltage signal VMID and to provide the boost of current required to charge the sensor.
In order to analyze the signal at the pin 204a (see e.g. FIG. 3a), the control unit 20 may comprise an analog-to-digital converter (ADC) 208a coupled to the pin 204a in order to sample the voltage of the oscillation. Thus, based on the resolution and sampling frequency of the ADC 208a, the whole oscillation may be characterized.
FIG. 4 shows an alternative approach. Specifically, the control unit 20a comprises a comparator 210a, which compares the voltage at the pin 204a with a reference signal, such as a reference voltage VRef. For example, this reference voltage VRef may be fixed, e.g. fixed to a voltage being slightly greater than VDD/2, or set via a digital-to-analog converter 212a. 
For example, FIGS. 5a and 5b show respectively the oscillations with and without a metallic object in the vicinity of the sensor 10. The reference voltage VRef and the output CMP of the comparator 210a is also shown in FIGS. 5a and 5b. 
Generally, the two approaches shown in FIGS. 3a and 4, i.e. the ADC 208a and comparator 210a, may also be combined in the same control unit 20a. 
Thus, based on the foregoing, contactless motion measurement may be achieved by interfacing LC sensors directly with microcontroller integrated circuits (ICs). Such sensing may be useful, e.g., for metering systems (gas, water, distance, etc.).
However, while handling and sampling sensors, microcontrollers (or MCUs) should reduce as much as possible the power consumption in order to permit the development of battery-powered systems.
Moreover, as MCU units are typically general-purpose, there is also the need to reduce as much as possible the silicon area due to the specialized circuits required for the implementation of the above functionality.
Accordingly, in LC sensor excitation and measurement techniques it is important to reduce consumption and cost, especially for battery powered applications as already mentioned.
For example, the measurement procedure applied in known approaches have a typical measurement time of around 50 μs, in which the excitation part, e.g. the generator of the voltage VMID, and the measurement part, e.g. the comparator or analog-to-digital converter, have to be switched on.
Thus, a first problem is related to the use of dedicated low power analog components for generating the voltage VMID and the internal reference voltage VRef, which results in a greater cost.
A second problem is related to the digital-to-analog converter 210a that has to be both low power and fast enough to follow the damped oscillation. This leads to significant power consumption per measurement and challenging application constraints in battery-powered systems.
Another critical aspect is that, depending on the specific sensor sizes to be supported, there could be the need to detect high frequency oscillations. Thus, in order to have enough flexibility to support a wide range of sensor sizes, a fast (and thus power consuming) comparator or analog-to-digital converter is required.